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21.
D.B. Dougherty 《Surface science》2006,600(19):4484-4491
The chemisorption of benzoate on a Cu(1 1 0) crystal at room temperature was studied using low temperature scanning tunneling microscopy. STM images, obtained at 5 K for low benzoate coverage, show isolated surface species that consist of a single Cu adatom stabilizing two benzoate molecules in a flat orientation. These species are discussed in relation to other known metal-organic surface compounds. At higher coverage the overlayer, called the α-phase, was also observed at 5 K and found to contain features attributable to two Cu adatoms associated with two pairs of non-equivalent benzoate species. The observed topographic features are used to suggest refinements of the structural model of the ordered α-phase overlayer. 相似文献
22.
通过测定全氟辛酸铵(APFO)、全氟辛酸三甲铵(TMHPFO)、全氟辛酸三乙铵(TEHPFO)在不同浓度NaCl (0.1, 0.3, 0.5 mol•L-1)存在时水溶液的表面张力曲线, 考察不同反离子的氟表面活性剂其表面活性随无机盐浓度的变化. 结果表明, NaCl对APFO的胶束化有明显的促进作用|对于TMHPFO和TEHPFO则在NaCl浓度较低时有很小的促进作用, NaCl浓度较高时由于Na+和N(CH3) (或N(CH2CH3) )之间的离子交换作用反而临界胶束浓度(cmc)增大. APFO, TMHPFO的最低表面张力(γcmc)随着NaCl浓度的增大而增大. 而对于TEHPFO, 少量NaCl的加入有利于降低γcmc、然后随着NaCl浓度的增大TEHPFO的γcmc增大. 这说明, 加盐溶液中始终存在着屏蔽效应和离子交换作用的竞争, 随着NaCl浓度增大离子交换趋势增大|对于疏水性较高的三乙铵离子在NaCl存在的情况下离子交换作用导致的γcmc升高需要更高的NaCl浓度才能显现. 通常认为外加无机盐是增强表面活性剂的表面活性的方法之一, 本工作表明, 对于有些反离子为有机阳离子的氟表面活性剂, 外加无机盐, 如NaCl, 不仅不能起到显著的增效作用, 浓度大时甚至会降低表面活性剂的效能. 所以这类表面活性剂在实际使用时应尽量避免高盐环境. 相似文献
23.
The phase and order behavior of charged asymmetric diblock-copolymer melts is studied by using coarse-grained molecular dynamics simulation. One of the blocks is made charged and other one is kept neutral, and the study systematically explores how the charged diblock-coploymer responses as the charge fraction of the charged block is varied from 10% to 50%. When charge fraction increases, the study finds ordered transitions from interconnected cylinder-like structures to lamellae, then to gyroid structures. It is also found that domain size of the obtained equilibrium morphology decreases slightly with the increase in charge fraction of the charged block. 相似文献
24.
Alexei Popov David A. Hoagland 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):3616-3627
A systematic capillary electrophoresis study uncovered how polyelectrolyte effective charge density varies with backbone charge spacing and solvent dielectric constant. The study primarily focused on aliphatic ionenes, a special class of polyelectrolytes, which possess regularly spaced quaternary ammonium groups in the backbone. Complete ionization of functional units and good solvency in water or mixtures of water with lower dielectric constant solvents (methanol, acetonitrile) enabled continuous measurements of ionene effective charge density through the onset of counterion condensation. Ionenes with both uniform and alternating charge spacing were examined. As expected, effective charge density rose linearly with fixed charge density to a critical value, above which effective charge density remained constant. Deviating from expectation, the onset of condensation did not occur at a critical fixed charge density. Instead, condensation initiated at a constant critical Bjerrum length. The same onset condition was found for quaternized poly(vinyl pyridine)s. These experimental results suggest a new form of condensation, one driven by ion-pairing of polyelectrolyte with counterions. In support of this hypothesis, the onset of condensation appeared to correlate with counterion size. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3616–3627, 2004 相似文献
25.
26.
以三乙胺为缚酸剂,通过苯甲酸同ω-(1H-1,2,4-三唑-1-基)-ω-溴化苯乙酮反应,合成了六种含三唑取代的苯甲酸甲酰甲酯类化合物,具有较高收率。 相似文献
27.
Densities, heat capacities and conductivities of water-surfactant--cyclodextrin (-CD) ternary systems were determined at 25°C. The surfactants studied were sodium dodecylsulfate (NaDS) and dodecyltrimethylammonium bromide (DTAB). From conductivity data, apparent critical micelle concentrations (cmc*) and degree of ionization of micelles were obtained at a fixed -CD concentration (mCD). From the cmc* value and that in water (cmc) the stoichiometry of the surfactant--CD complex was calculated. At a given mCD, the apparent molar volume V,CD and heat capacity C,CD of -CD in the two surfactants were calculated as functions of surfactant concentration mS. For both NaDS and DTAB, V,CD increases with mS up to about the cmc beyond which it decreases to a constant value at high mS, the opposite is observed for C,CD. With NaDS, a jump in the C,CD vs, mS trend was detected and ascribed to a structural NaDS micellar transition. The apparent molar volume VS and heat capacity CS of NaDS and DTAB in the water--CD mixture 0.017 m were also obtained. From these properties and those in pure water, the volume VS and heat capacity CS of transfer of the surfactant from water to water+-CD mixture as functions of mS were calculated. For both surfactants, the VS vs. mS trends increase to the cmc and then decrease in a monotonic manner, whereas CS increases regularly with mS in the pre-micellar region and is essentially constant in the post-micellar region. The VS vs. mS trends were qualitatively explained in terms of dispersed, complexed and micellized surfactant contributions. 相似文献
28.
The steroids were derivatised with aroyl chloride to yield the corresponding benzoates. Among them, their 4-methoxybenzoates were obtained in greatest yield and were analyzed by HPLC with the smallest detection limit (10 ng) by means of a UV detector (254 nm). This method of derivatization can be applied for analysis of steroids and triterpenoids from crude products with the HPLC technique. 相似文献
29.
R. De Lisi B. Marongiu S. Milioto B. Pittau S. Porcedda 《Journal of solution chemistry》1997,26(9):889-911
Specific conductivities, densities, heat capacities, and enthalpies of dilution at 25‡C were measured forN,N,N-octylpentyldimethylammonium chloride (OPAC) in water-urea mixtures at various urea concentrations mu as functions of the surfactant concentration ms. From conductivity data, the cmc and the degree of the counterion dissociation Β of the OPAC micelles were calculated. The
cmc increases linearly with increasingm
u
while Βvs. mu is a smooth concave curve. From the experimental thermodynamic data, the apparentY
Φ
and partialY
2
molar properties (volumes, heat capacities, and relative enthalpies) are derived as functions of mu andm
s
. The effect of urea on the dependences of the different properties on ms are discussed. From data in the premicellar region the standard partial molar volumesV
2
0
and heat capacitiesC
p2
0
were evaluated. It was observed thatV
2
0
increases linearly withm
u whileC
p2
0
decreases. The properties of OPAC in the dispersed and micellized forms at the cmc were obtained and, therefore, the thermodynamic
functions of micellization were calculated on the basis of the pseudo-phase transition model. 相似文献
30.
The solid state thermal behavior of trans-[Co(bpb)(amine)2]NCS⋅H2O complexes where (bpb)=[N,N’-bis(2-pyridinecarboxamido-N)-1,2-benzene], and amine=pyrrolidine (prldn)(1), and benzylamine (bzlan) (2), and trans-[Co(bpb)(piperidine)2]ClO4⋅H2O (3) (mixed with KSCN), has been studied using thermoanalytical techniques, infrared spectroscopy, and pyrolysis coupled
to both infrared and mass spectrometry, PY/FTIR and PY/MS. The deamination-anation reaction is clearly observed for all three
complexes. The estimated values of E
a for the deamination-anation are: E
a(1)=246.8 kJ mol−1, E
a(2)=255.7 kJ mol−1, E
a(3)=234.7 kJmol−1. The trend in E
a values is rationalized based on the ligand field strength of the amines and the structural effects. A novel decarbonylation
of the amide CO group from the equatorial ligand is observed after the release of one amine molecule. This process has been
monitored for complex (1) by FTIR in the carbonyl region and by mass spectrometry for the detection of CO2 at 280°C. The activation energy of this process is estimated for complex (1) (662.5 kJ mol−1). The reaction scheme for the observed reactions is proposed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献